This invention relates to a non-ballistic type dot matrix wire print head apparatus. Dot matrix wire print head apparatus may be generally classified as being of the ballistic type wherein the print wire members are not connected to the drive armatures and are driven by impact with the drive armatures, or the non-ballistic type wherein the print wire members are fixedly connected to the drive armatures so that the print wire members and armatures have unitary movement. While the features of the present invention are disclosed in conjunction with a non-ballistic type print head assembly, certain features may also be utilized with a ballistic-type print head assembly.
In prior art ballistic-type apparatus, such as that disclosed in U.S. Pat. Nos. 4,230,038, 4,230,412, 4,185,929 and 4,478,528, the disclosures of which are incorporated herein by reference, wire type printing members (stylus or styli) are arranged in spaced relationship about a central longitudinal axis in a generally circular or elliptical matrix for reciprocable movement between a non-print position and a print position with the movement from the non-print position to the print position being of ballistic nature, i.e. by impact and/or driving engagement with another moving member. Each printing member is operatively associated with a radially innermost portion of a radially outwardly extending armature member and ballistically driven thereby by impact therewith during pivotal movement of the armature from a non-print position to a print position. A radially outermost portion of each armature is operatively associated with a radially outwardly located and circumferentially spaced electromagnetic means having radially spaced pole portions including a radially innermost pole portion and a radially outermost pole portion, the pole portions including flat coplanar radially spaced and radially extending end surfaces which face away from the direction of movement from the non-print position to the print position and engaging a side surface of the armature at various times.
In some types of the prior art ballistic-type apparatus, the construction and arrangement is such that the armature is pivotally supported at all times on a radially outermost edge of the end surface of the radially outermost pole portion and impacts the end surface of the radially innermost pole portion which is constructed and arranged to cause pivotal movement of the armature from the non-print position to the print position by magnetic attraction. In addition, the construction and arrangement is such that the armature impacts on the end surface of the innermost pole portion at approximately the same time that the printing member is being driven toward the paper. The result is that the kinetic energy of the armature is lost and only the kinetic energy of the printing member is thereafter effective to cause completion of the printing operation. The lost kinetic energy is simply dissipated upon impact with the surface of the pole portion with resultant high levels of noise and heat. In addition, the speed of the printing process is reduced and the number of sheets of paper which can be printed at one time is also limited. Furthermore, in order to obtain sufficiently high levels of kinetic energy to produce satisfactory printing results, relatively high levels of energy must be used to operate the electromagnetic means.
In the invention disclosed in U.S. Pat. No. 4,230,038, the armature members and the electromagnetic means are constructed and arranged so that the armature members are normally pivotally supported by a first pivot means on a radially innermost edge of a radially innermost pole portion while being magnetically attracted by a radially outermost pole portion. In addition, the pole portions are constructed and arranged so that the end surfaces thereof face toward the direction of movement of the armature and the printing members from the non-print position to the print position. As a result, the driving movement of the armature continues after impact with the end surface of the outermost pole portion without loss of a substantial portion of the kinetic energy thereof as in prior art apparatus. Furthermore, the construction and arrangement is such that after impact of the armature with the end surface of the outermost pole portion, the first pivot means is disengaged and a second pivotal means is provided between a radially outermost portion of the armature and the radially outermost edge of the radially outermost pole portion whereby the driving movement of the armature may continue substantially unimpeded until completion of the printing operation.
For many years, there has been a trend toward the use of smaller size, dot matrix print head assemblies operating at relatively high speeds with maximum efficiency. There has also been a trend toward use of more print wire members in each dot matrix print head assembly and dot matrix print assemblies having at least 18 or more print wire members has become commonplace. It is often desirable to reduce the size of the print head assemblies which results in difficulty of assembly, repair and maintenance and increased costs of manufacture. At the present time, there is a need for a relatively low cost and relatively small size, yet highly efficient, dot matrix print head assembly which is easy to assemble and be mounted on a printer mechanism.
Objects of the present invention are to provide a high speed, reliable, efficient, compact, lightweight, low cost and easily manufacturable dot matrix print head assembly. The invention provides a dot matrix print head assembly which (1) reduces the mass of moving parts; (2) reduces print wire resonances; (3) employs a laminated electromagnet construction with improved flux concentration and low inductance and low current; and (4) employs an armature and pole construction.
Another object of the present invention is to provide a relatively small size, e.g. approximately 2 inch diameter by 11/2 inch length, print head assembly with a relatively large number of print wires, e.g. 24 print wire members. It is also an object of this invention to provide a construction and arrangement which enables the parts to be manually assembled with a minimum of time and effort while also providing maximum accuracy of critical relationships between the operational components.